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Homestead Chimney Service Blog

Time to Think About Sealing Your Chimney Crown

A chimney crown, also called a chimney wash, is the top portion of a masonry chimney. The crown covers and seals the top of the chimney, extending from the flue liner to the edge of the chimney. Its downward slope directs water from the chimney flue to the edge of the crown itself. A masonry chimney usually has an inadequate crown if it’s made from a common mortar mixture.

Re-sealing a chimney crown - before and after

Re-sealing a chimney crown – before (left) and after (right)

A higher-quality crown is normally done by a chimney specialist who understands the type of mortar and concrete that is best for this tough job. The crown is formed or cast to provide an overhang that projects at least two inches beyond each side of the chimney. The chimney flue liner tile should project at least two inches above this crown. The crown needs to withstand abuse from weather elements without deteriorating, chipping, or cracking.

Sealing the chimney crown involves applying a flexible coating of acrylic to protect the crown from water infiltration. If a crown becomes cracked, water can enter the chimney and, as the crack widens over time, more water is permitted access. Eventually, the amount of water entering the chimney exceeds the amount that can evaporate and the deterioration process begins. If damage is caught early, the crown can be repaired and a masonry sealer can be applied to the chimney.

The rubber-like coating of the sealer fills in cracks in the crown. Since it is flexible, it can expand and contract with the chimney. It also directs water away from the top of the chimney, serving as an umbrella. This material can be applied to other exposed masonry surfaces to prevent water from entering through the chimney sides.

If your chimney crown has not been addressed, have a chimney inspection to identify whether sealing is necessary. A darkened upper masonry chimney, flaking and chipping of bricks, or dark mold on a stone chimney are typical indications that the area requires repair. Addressing damage before it becomes serious will save time and money.

The Damage Water Can Do to a Masonry Chimney

Water is essential for human life, but it can severely damage a chimney. Most homeowners assume that their chimneys will last forever without any regular maintenance and in some cases, a chimney will last a long time. However, exposure to harsh weather can cause deterioration that turns the chimney into a safety hazard.

Water damaged masonry chimney

Despite its simple appearance, a chimney is actually quite complex. Transporting air to and from the fireplace is just one of its important functions. Brick, concrete, stone, mortar, cast iron, and steel are some materials used to make masonry chimneys. Most of these are adversely affected when they come in direct contact with water or are penetrated by water. Loose masonry materials, damaged lining systems , and flue obstructions make the chimney a hazard for home occupants.

Prolonged contact with water causes accelerated deterioration of all materials used to make a masonry chimney, except stone. Seasonal freezing and thawing allows moisture to contract and expand, creating stress on masonry materials. When water creeps into the chimney, it can rust cast iron or steel. This weakens or destroys the metal areas of the chimney.

Water penetration may damage both the interior and exterior of a masonry chimney. It can decay exterior mortar and deteriorate or crack the flue liner. Water can rot wood adjacent to the chimney and deteriorate a masonry or metal firebox. It can even rust the damper and deteriorate a central heating system. Water may travel through the chimney and into the home, staining ceilings and walls.

Installing a chimney cap is one of the least expensive ways to prevent water damage to a chimney. Per specifications from Underwriters Laboratories (UL), a UL-listed chimney lining system must have a chimney cap. This cap prevents rainwater, snow, and other airborne moisture from entering the flue and traveling into the chimney interior where it can cause damage.